The mystic sound Aum is explained in detail in the Mandukya Upanishad. Sanskrit text...

Aum

O gods, with our ears may we hear that which is auspicious…

Adorable Ones, with our eyes may we see that which is auspicious. While praising the gods, with steady limbs may we enjoy the life that is allotted by the gods. May Indra of ancient fame be auspicious to us. May Pusan and the Visva-Devas be propitious to us. May Tarksya of unhampered movement, be well disposed towards us. May Brihaspati ensure our welfare. Aum! Peace! Peace! Peace!

1. Aum this syllable is all this… An explanation of that… All that is past, the present and the future, all this is the syllable Aum. And whatever else there is beyond the threefold time, that too is only the syllable Aum.

2. All this is verily Brahman. This self is Brahman. This same self has four quarters.

3. The first quarter is Vaishvanara, whose sphere is the waking state, who cognises extemal objects, who has seven limbs and nineteen mouths and who experiences gross objects

4. The second quarter is Taijasa, whose sphere is the dream state, who cognises internal objects, who has seven limbs and nineteen mouths, and who experiences the subtle objects.

5. Where one being fast asleep does not desire any desire whatsoever and does not see any dream whatsoever that is deep sleep. The third quarter is prajna, whose sphere is the state of deep sleep, who has become one, who is verily a mass of cognition, who is full of bliss and who experiences bliss, whose face is thought

6. This is the lord of all. This is the knower of all. This is the inner controller. This is the source of all. This is the beginning and the end of beings.

7. Turiya is not that which cognises the internal, not that which cognises the external, not what cognises both of them, not a mass of cognition, not cognitive, not non-cognitive. lt is unseen, incapable of being spoken of, unnameable. the essence of the knowledge of the one self that into which the world is resolved, the peaceful, the benign, the non-dual, such they think, is the fourth quarter. He is the self: He is to be known.

8. This is the self which is of the nature of the syllable Aum, in regard to its elements. The quarters are the elements, the elements are the quarters, namely the letter ‘a’, the letter ‘u’ and the letter ‘m’.

9. Vaishvanara, whose sphere is the waking state, is the letter ‘a’, the first element, either from the root ‘ap’ to obtain or from being the first. He who knows this obtains verily, all desires. Also he becomes first.

10. Taijasa, whose sphere is the dream state, is the letter ‘u’. It the second element, from exaltation or inter-mediateness. He who knows this exalts, verily, the continuity of knowledge and he becomes equal: in his family is born no one who does not know Brahman.

11. Prajna, whose sphere is the state of deep sleep, is the letter ‘m’, the third element, either from the root ‘mi’, to measure or because of merging. He who knows this measures all this and merges also.

12. The fourth is that which has no elements, which cannot be spoken of, into which the world is resolved, benign, non- dual. Thus the syllable ‘Aum’ is the very self. He who knows it thus enters the self with his self.

Yamunashtak is a a 9 versed Sanskrit poem by Mahaprabhu Vallabhacharya. His collective work in poetry is known as Shodash Granth. His followers are known as Pushtimargi Vaishnavas. Reading the Yamunashtak and praying to Yamuna Maharani helps in winning over personal weaknesses, suggests, the 16th century Bhakti saint, Mahaprabhu Vallabhacharya... More...